The present invention relates to a method of producing Ndxe2x80x94Fexe2x80x94B based nanophase powder, or more particularly, to a method of producing Nd2Fe14B phase powder of 1 xcexcm or less, comprising Nd2Fe14B crystal grains of 50 nm or less, by means of a mechano-chemical process.
In general, a permanent magnet is a material maintaining a magnetic field within the material in itself even after the removal of the externally-applied magnetic field. As such, it is necessarily used in motors, generators, electronic equipment, etc.
In particular, permanent magnets are utilized in high value-added products such as video recorders, computer disk drives, and electric motors, which are applicable in a variety of industries, and these magnets have a decisive effect on the quality and performance of the final product.
For the alloys of the conventional permanent magnets, the alnico and ferrite have been mainly used. However, with the trend towards compactness and high-performance of electronic, communications, and mechanical components, Ndxe2x80x94Fexe2x80x94B based materials which have superior magnetic characteristics have been extensively used in recent years.
Ndxe2x80x94Fexe2x80x94B based magnets are classified into sintered magnets which were developed in Japan, and the bond magnets which were developed in the United States. With respect to the method of producing sintered magnets, an alloy in the form of ingots is first prepared by means of casting, followed by powder making process with a sequential crushing and pulverization of the ingots.
Then, a magnet in form is produced by molding the alloy powder in the magnetic field, followed by sintering and heat-treatment. Consequently, in order to produce the magnet, powder making process of the Ndxe2x80x94Fexe2x80x94B based alloy is necessary. The rapid cooling-solidification method which is used in the powder production method developed in the United States does have an advantage of producing materials of fine crystal grains. However, it has a disadvantage of deteriorating purity by being easily contaminated during the ribbon production and milling process. Further, there is a difficulty in general powder molding, which leads to necessitating molding with mixing of bonding agents, or molding by hot pressing.
Moreover, the ingot-crushing method, which is the powder production method developed in Japan, is a long and complicated process, in which the fine powder can be obtained is possible only after the numerous steps after the production of ingots. In addition, this process is long and has a limitation to obtain fine grain sized powder by pulverization.
Accordingly, in solving the aforementioned problems, the technical objective of the present invention lies in providing a method of producing nanophase powder without the mechanical crushing and pulverization process.
In achieving the aforementioned technical objectives, the present invention comprises the following steps of:
(a) Producing a Ndxe2x80x94Fexe2x80x94B composite oxide powder;
(b) Producing a composite powder of Nd oxides and xcex1-Fe by means of reducing said Ndxe2x80x94Fexe2x80x94B composite powder;
(c) Ball-milling said composite powder of Nd oxides and xcex1-Fe into fine particles;
(d) Forming Nd2Fe14B and CaO by means of molding with a mixture of Ca powder and said composite powder particles, and then reducing the Nd oxides therein by heat-treatment in argon atmosphere; and
(e) Producing the powder of a single phase of Nd2Fe14B by means of removing the CaO by-products by washing with water, followed by drying.